A Contribution to the Physical History of the Cretaceous Flints

Abstract

Some years ago, whilst endeavouring to clear up the obscure points in the history of the Cretaceous flints, I naturally turned for guiding data to such analyses as were forthcoming of the Chalk and Globigerine ooze of the Atlantic. But the further my inquiries were pursued in this direction, the stronger grew my conviction that no more fallacious test of the percentage of silica originally present in the White Chalk could be resorted to than that of assuming as a standard the percentage it now contains, and hence that any comparison of the calcareous mud with the ancient Chalk, instituted with the view to determine this percentage, must necessarily prove equally fallacious. This result, however, was only to a certain extent unlooked for, inasmuch as I had long previously suspected, on entirely distinct grounds, that the almost complete absence of silica in the flint-bearing Chalk did not arise from any deficiency in it of that substance whilst it was yet in a plastic state at the bed of the ancient sea, but was due to certain special conditions, which led not only to the continuous elimination of the siliceous material for a time mechanically associated with the calcareous mud, but to its consolidation in the stratified layers alternating with the Chalk, which constitutes by far the most striking and, at first sight, unaccountable feature in this formation. In directing attention, at the outset of my observations, to the writings of those who have preceded me in this line of inquiry,